Which web browser is the safest? Current trends show over 50% of malware infections occur via Internet download. During Q1, 2009 NSS Labs performed the industry’s first comprehensive test of web browser protection against socially engineered malware. This report examines the ability of six different web browsers to protect users from this leading threat. The results are based upon empirically validated evidence gathered by NSS Labs during 12 days of 24x7 testing of more than 154,000 individual tests.

If I download anything it is usually in Firefox, not only does its download manager initiate an automatic virus scan, I have NoScript, ABP, WOT & Site Advisor. That with SpywareBlaster gives me some protection.

IE8
To be honest the IE8 smart screen filter is great. IE8 was also the first to protect against cross site scripting. When it runs with lowest rights in Vista or Win7 (with DEP ADSLR and SEHOP etc). I do not understand why IE8 does not has the option enabled

The first is an important precaution against clickjacking (scripts) / hidden windows, the second against drive by downloads.

Chrome
I personally think Chrome is the safest browser, reasons
- internal sandbox
- option to run plug-ins sandboxed (--safer-plugins)
- Javascript is assembled into machine code with hidden classes instead of shared dictionaries, assembled code is allways more restricted than interpretated commands (and it is a lot faster).

To match up against IE8's smartscreen you need to add the extentions Wot and SiteAdvisor.

Have a look at the newest chomium builds, besides cookie, pictures, plug-ins, pop-ups and javascript, you can also specify to deny IP localisation tracking (so when a website tries to figure out where your IP is from).

Unless the other browser redefine their architecture, chrome will only create more distance between itself and others

there is no 100 percent browser. The safest browser is a browser which is run
in a sanbox ie sandboxie. there is no need to restrict yourself to a certain browser if you want to use another browser when we have sandbox and hips programs.

that said firefox does have a lot of security and privacy add on's like in my sig.

I'd say IE8 is more secure than Firefox out of the box. Tweak it to auto-start in private browsing mode and in private filtering, combined with the smart screen filter and it's a nice browser. Once you customize FF with addons though it becomes very safe and functional. I've been using it for so long I'm just comfortable with it now, but I'd feel perfectly safe with IE... they've come a long way.